Re: [lkp-robot] [bisect done] e71e836f46 [ 17.567570] WARNING: CPU: 0 PID: 1 at arch/x86/include/asm/pgtable.h:540 __change_page_attr_set_clr

[Fengguang Wu]

Hi Dave,

On Tue, Apr 10, 2018 at 01:59:21PM -0700, Dave Hansen wrote:
> On 04/09/2018 06:12 PM, kernel test robot wrote:
> > +-----------------------------------------------------------------------+------------+------------+------------+------------+
> > |                                                                       | 64c8075940 | e71e836f46 | 0564258fb2 | 87e1e2f51c |
> > +-----------------------------------------------------------------------+------------+------------+------------+------------+
> > | boot_successes                                                        | 35         | 0          | 19         | 11         |
> > | boot_failures                                                         | 0          | 26         |            |            |
> > | WARNING:at_arch/x86/include/asm/pgtable.h:#__change_page_attr_set_clr | 0          | 26         |            |            |
> > | RIP:__change_page_attr_set_clr                                        | 0          | 26         |            |            |
> > +-----------------------------------------------------------------------+------------+------------+------------+------------+
>
> LKP folks, does this mean that the system didn't boot in all the places
> that we saw this warning?  Or does this just say that it *had* the
> warning 26 times?

The 'e71e836f46' column means there are 0 boots (sorry boot_successes
might be a bit confusing) with clean dmesg and 26 boots with
warning/error dmesg. It indicates that WARNING is 100% reproducible.

       boot_successes + boot_failures = total test boots

> I looked into this a bit.  This LKP report points the finger at this
> commit which trips over a new debugging WARN_ON() I added:
>
> [patch 06/11] x86/mm: Remove extra filtering in pageattr code
>
> It's because set_memory_nx() encounters the (unsupported) _PAGE_GLOBAL
> bit while clearing _PAGE_NX.  I never saw this in testing because this
> patch:
>
> [PATCH 10/11] x86/pti: never implicitly clear _PAGE_GLOBAL for kernel image
>
> explicitly clears out _PAGE_GLOBAL long before the set_memory_nx() call.
> So I *think* this is a transient issue resulting in bad ordering of the
> _PAGE_GLOBAL patch set.  I believe it is harmless.

Right. The '0564258fb2' and '87e1e2f51c' columns mean the
'tip/x86/pti' and 'tip/master' branch HEADs boot clean.
So it's a transient warning inside the branch.

Thanks,
Fengguang